The hydrocarbon carcinogens have been implicated as a possible cause of cancer of the colon. Most of these compounds are relatively inactive until they are converted to the reactive epoxide form in the target cell. This conversion is enzymatic and the major enzyme involved is aryl hydrocarbon hydroxylase (AHH). AHH is an inducible enzyme, and we have demonstrated that the degree of inducibility varies widely in a normal human population. We have further shown that AHH inducibility is related to occurrence of bronchogenic carcinoma. Assay for AHH activity is carried out in cultured lymphocytes obtained from peripheral blood. The enzyme also occurs in a number of other tissues of the body including colon. The aims of the project are: 1. To determine whether there is a relationship between degree of AHH inducibility and the occurrence of carcinoma of the colon. 2. To modify the method, developed in our laboratory for assay of AHH in peripheral blood for adaptation as a routine clinical laboratory procedure. Also, to develop and improve methods for certain of the other hydrocarbon metabolizing enzymes, particularly those which catabolize the epoxides. 3. To compare activities of these carcinogen-metabolizing enzymes in peripheral blood cells, colon, and other tissues. 4. To investigate the effects of inherently different amounts of these enzyme activities upon rates of incorporation of carcinogen metabolites into cell components and the effects of these metabolites on cell activities, particularly DNA repair and in vitro transformation.